I used my Fuji X-T1 professionally for several years (for architectural and commercial photography), but I've not digi-scoped with it. It's old and only 16mpx, but now I'm retired every time I think about updating it I can find no good reason. You can get hold of a good one for $300. I imagine you can get a good used X-T2 (24mpx) for under your budget. They are a joy to use, ergonomically, and have a larger sensor than some of the recommendations you've had so far.
I swapped my top of the range Nikon DSLR for the Fuji and before that I used Canon... in general, IMHO, Fuji and Sony lead the mirrorless pack, with Panasonic and Olympus close behind (look out for those small sensors though). No need to feel bad about not being able to afford Nikon and Canon (traditionally the two most-used professional SLR/DSLR camera brands), since with mirrorless they're now playing catch-up, while charging customers a premium for the privilege.
Just my opinions of course. Good luck.
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